A captive helicopter is a helicopter which is tethered to the
ground with a rope, as with a captive balloon. Captive helicopters
can be used for the same purposes as captive balloons. They are
easier to steer than a regular helicopter.
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The suffix of "captive" is "-ive".
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A portal is a hole.
A portal exit is where you exit out of the hole.
A portal entrance is where you enter into the hole.